Reduced Sensitivity in Monilinia fructicola to Propiconazole Following Prolonged Exposure in Peach Orchards

Abstract

The baseline sensitivity of Monilinia fructicola in a peach orchard not previously exposed to demethylation-inhibiting (DMI) fungicides was determined for propiconazole, using the concentration in an agar medium required to suppress radial growth of mycelium by 50% (EC50) The baseline sensitivity was found to be approximately 0.03 μg/ml. Prolonged, regular exposure of the natural population of M. fructicola to propiconazole in the test orchard over a 3-year period (29 total applications) resulted in a wider range of sensitivity (EC50 of 0.02 to 2.16μg/ml) among isolates than was observed in the initial population (EC50 of 0.02 to 0.15 μg/ml). Comparisons with isolates from commercial orchards where DMI fungicides were used regularly showed that sensitivities were comparable to, or less than, those of isolates from the population in the test orchard that had been exposed to propiconazole for the 3-year period. M. fructicola in South Carolina peach orchards might now be less sensitive to DMI fungicides than when those fungicides were first introduced for brown rot control, although effective disease control in the field has been maintained.

Toxicity of mancozeb, chlorothalonil, captan, fluopyram, boscalid, and difenoconazole toDidymella applanataisolates from Serbia

“…[19][20][21][22][23] The EC 50 values of this fungicide, established by Stevi c et al [24] for Serbian Venturia inaequalis isolates, were between 0.016 and 0.362 mg L ¡1 . Their study showed that nine V. inaequalis isolates were moderately resistant (RF D 5.1-16.1), and one isolate was resistant to difenoconazole with RF of 22.6.…”

Propiconazole Sensitivity in Populations of Geotrichum candidum, the Cause of Sour Rot of Peach and Nectarine, in California

“…However, to establish a discriminatory dose that differentiates between baseline (i.e., never exposed to propiconazole) and resistant isolates associated with a control failure, a more comprehensive analysis of field isolates will be needed. For example, a discriminatory dose of 0.3 |ig/ml was established to monitor resistance to propiconazole of M. fructicola, which was 10-fold greater than that of the baseline population (10,42). This is the first report of reduced sensitivity to propiconazole in G. candidum in natural populations occurring in a postharvest setting.…”

“…Propiconazole in a different formulation (Tilt; Syngenta Crop Protection) has been and continues to be used as a preharvest treatment to control brown rot caused by M. fructicola. Resistance to propiconazole in M. fructicola has been reported in the southeastern United States (10,31,42) but there are no reports of crop loss or reduced sensitivity of pathogen populations to pre-or postharvest use of propiconazole in California.…”

Toxicity of copper hydroxide, dithianon, fluazinam, tebuconazole and pyraclostrobin toDidymella applanataisolates from Serbia

“…Indeed, resistance to DMIs has been reported in many different phytopathogenic fungi including Monilinia fructicola, Venturia inaequalis, Podosphaera xanthii, Uncinula necator, Sclerotinia homoeocarpa, Cercospora beticola, etc. [30][31][32][33][34][35] All D. applanata isolates from Serbia were sensitive to tebuconazole with RFs less than 1.9. Even though resistant isolates were not detected in the present study, reported cases of DMI resistance development in the aforementioned plant pathogens imply necessity of establishment of a regular monitoring program for early detection of resistant strains in pathogen's population.…”